Abstract
The microbial aminopeptidase may be composed of two similar, if not identical, chains, each containing 1 super-reactive and essential tyrosine residue/protein unit of mol. wt. 30 000. A similar result was obtained with aminopeptidase from pig-kidney particles (Wachsmuth, 1967), which was found to contain 10 essential and super-reactive tyrosine residues/mol. (mol.wt. 280 000) or only 1 tyrosine residue/sub-unit. Additional experiments, involving in each case the isolation and characterization of the radioactive iodinated tyrosine peptide, are clearly necessary before the sub-unit structure of the aminopeptidases is further established.